Update on the global distribution of genotypes of wild type measles viruses

Applicability of oral fluid collected onto filter paper for detection and genetic characterization of measles virus strains

Expansion of measles molecular surveillance to developing countries where measles is endemic will help facilitate measles control. Limited infrastructure in these areas is a barrier to referral of specimens suitable for measles virus (MV) genotyping. In this study, we demonstrate that oral fluid dried onto filter paper can be used for the detection and characterization of MV strains. Using this approach, an MV-positive sample by reverse transcriptase PCR could be obtained from 67% of serologically confirmed acute measles cases. Mimicking certain environmental conditions and duration of transportation established that MV RNA remained detectable and suitable for nucleic acid sequencing in oral fluid spots for at least 1 week. In the context of a measles outbreak in a remote region of the world where infrastructure is poor, oral fluid samples dried onto filter paper and sent to a specialized laboratory for testing will aid in the identification and characterization of the causative MV strain.

Genetic characterization of measles viruses isolated in Turkey during 2000 and 2001

BACKGROUND

Molecular epidemiologic studies have made significant contributions to measles surveillance activities by helping to identify source and transmission pathways of the virus. This report describes the genetic characterization of wild-type measles viruses isolated in Turkey in 2000 and 2001.

RESULTS

Wild-type measles viruses were isolated from 24 cases from five provinces in Turkey during 2001. The viruses were analyzed using the standard genotyping protocols. All isolates were classified as genotype D6, the same genotype that was identified in Turkey in previous outbreaks during 1998.

CONCLUSION

Turkey has begun implementation of a national program to eliminate measles by 2010. Therefore, this baseline genotype data will provide a means to monitor the success of the elimination program.

Development of a semi-quantitative real-time RT-PCR for the detection of measles virus

Real-time detection of polymerase chain reactions allows convenient detection and quantification of virus-derived nucleic acids in clinical specimens. We have developed a real-time RT-PCR assay for the detection of measles virus (MV) genomic RNA, and compared it to a well-established conventional RT-PCR assay. Based on a serial dilution of the live-attenuated MV Edmonston Zagreb vaccine, the detection limits were approximately 0.1 and 0.02 cell culture infectious dose 50% units (CCID50) per test for the conventional and TaqMan RT-PCR assays, respectively. Furthermore, tissue materials spiked with known quantities of MV were equally well detected in both assays. The TaqMan assay was linear within a range of 10(4.4) to 10(-0.6)CCID50/ml, with an intra-assay variability lower than 3% and an inter-assay variability ranging from 1.5% at 10(4.4)CCID50/ml to 8.7% at 10(-0.6)CCID50/ml. The TaqMan assay could detect representative wild-type viruses from the currently active MV clades, and could detect MV genome in clinical specimens obtained from measles patients. Finally, quantification of MV RNA in peripheral blood mononuclear cells or broncho-alveolar lavage cells from cynomolgus macaques collected at different time points after experimental infection showed a good correlation with virus isolation data. In conclusion, the TaqMan assay developed is specific, sensitive, rapid and reproducible, and can be of use for diagnostic purposes or for studies on the pathogenesis of measles.

[Contribution of unvaccinated siblings to a measles outbreak in Switzerland]

BACKGROUND

A measles outbreak occurred in Geneva between March and July 2003. An investigation was conducted to determine its magnitude, identify predominant modes of transmission, and assess disease outcome.

METHODS

In Switzerland, measles notification has been mandatory for physicians since 1999 and laboratories since 1988. All cases were investigated and followed up by interviewing physicians using a standardized questionnaire. Viral genotype was determined for 4 cases using a saliva specimen processed at the Robert Koch Institute, Berlin. Geographic distribution of cases and vaccination coverage were compared.

RESULTS

Overall, 54 cases were notified. Fifty-three cases were between 10 and 19 years of age. Ninety-four percent (n = 46) of 49 cases with known vaccination status were not vaccinated and none were fully immunized (2 doses). Measles complications occurred among 19% (n = 7) of the 36 patients with follow up information: pneumonia (n = 4, combined with pericarditis and hepatitis in one case) and bronchitis (n = 3). Three persons were hospitalized. No complication was reported among 3 persons partially vaccinated (1 dose). The virus belonged to genotypes D8 and D5. Five separate clusters of related cases included 74% of all cases. Transmission mainly occurred within families (43% of all cases) and school (28%). Two of the most affected areas had measles vaccination coverage well below the cantonal average.

CONCLUSION

Low vaccination coverage combined with clusters of unvaccinated household contributed to continued virus circulation and represents a threat to the canton of Geneva as new outbreaks of measles may reoccur.

Measles virus genotype B2 is not inactive: Evidence of continued circulation in Africa

This study describes two measles outbreaks--one in Cape Town, South Africa in November 2002, and the other in Luanda, Angola in March 2003. The outbreaks were notable because they were caused by closely related genotype B2 viruses. This genotype was first described in an outbreak in Libreville, Gabon in the 1980s and was labeled as inactive by the World Health Organization in 2003 because it had not been detected for over 15 years. As the first three cases in the Cape Town outbreak were Angolan citizens who recently arrived from Angola, it appears likely that the source of the virus was Angola. Molecular analysis of specimens collected during the outbreak in Luanda provided direct evidence for the circulation of genotype B2 measles virus (MV) in Angola. This study clearly demonstrates that there is still active circulation of genotype B2 in Africa, and we propose that its apparent inactivity is merely the result of insufficient virologic/molecular surveillance in the region. These findings highlight the need for expanded molecular surveillance in Africa.

Laboratory investigations are indispensable to monitor the progress of measles elimination--results of the German Measles Sentinel 1999-2003

BACKGROUND

The elimination of measles is a goal set by the World Health Organisation to be reached by 2010 in the European region.

OBJECTIVES

To enhance the measles surveillance in Germany, a country-wide laboratory supported a sentinel was established.

STUDY DESIGN

A network of >1200 representatively distributed practitioners reported detailed data on all clinically diagnosed cases and provided specimens for laboratory diagnosis.

RESULTS

A total of 3225 suspected cases were reported between October 1999 and December 2003. The incidence in Western Germany decreased from >15 cases per 100,000 population to one case in 2003, while in Eastern Germany <1 case per 100,000 population was observed during these years. Laboratory investigations were undertaken in 40% of cases in 2000/2001. This rate increased to 79% in 2003. Simultaneously, the rate of confirmed cases dropped from 60% in the former years to 23% in 2003. Measles virus (MV) detection by serology and by PCR revealed concordant results in 92%. Most suspected cases (85%) were unvaccinated with 66% being laboratory confirmed. Only 10% of suspected cases occurred in vaccinated individuals and very few (22%) could be confirmed. Analyses of confirmed measles in vaccinated patients (n = 49) revealed 24.5% primary vaccine failures, 24.5% reinfections after successful vaccination and 31% MV infection before or shortly after vaccination. The genetic characterisation of 389 MV isolates identified eight genotypes: B3, C2, D4, D5, D6, D7, G2 and H1. Only the C2, D6 and D7 MV genotypes circulated endemically in Western Germany. The newly emerged MV D7 almost completely replaced the pre-existing C2 and D6 MVs in 2001. The few measles cases detected in Eastern Germany were mostly caused by imported MVs.

CONCLUSION

The data demonstrate that laboratory investigations including molecular methods are an indispensable tool for surveillance in all countries advanced in measles elimination.

Measles virus genotype circulation in Spain after implementation of the national measles elimination plan 2001-2003

Molecular characterization of measles virus is important for disease surveillance and for monitoring elimination of the virus throughout the world. Furthermore, knowledge of genotype distribution in as many countries as possible, is useful for tracing the origin of a strain, especially in countries without endemic measles disease, where most cases are imported. Data on genotypes circulating in Spain from 1970 to 1997 showed the prevalence of genotypes C1, C2, and D6, with subsequent replacement of each other. After the establishment of the Spanish Measles Elimination Plan, genotyping with a new retrotranscriptase polymerase chain reaction (RT-PCR) was undertaken directly on 92 specimens, corresponding to 90 patients, which were positive for measles by a different diagnostic RT-PCR. Genotypes B3, D4, D8, A, C2, H1, and D7 were found in different autonomous communities (Madrid, Balearic Islands, Valencia Community, Extremadura, Andalusia, Canary Islands and Murcia) between 2001 and 2003 with none of these genotypes being prevalent. After the introduction of the vaccine in 1978, the incidence of the disease decreased from 150,000 cases in 1977 to 64 in 2002. This could be the reason for the change observed in the pattern of measles genotype circulation, since this pattern was reported in countries at an advanced stage of eradication of measles. This report considers that Spain is on the way to eradicating measles.

Surveillance of measles in the Sudan using filter paper blood samples

Dried blood spots collected on filter paper are considered potential clinical specimens for measles surveillance because of their ease of collection, storage, and transport. The usefulness of these samples for surveillance of measles was evaluated in a field setting. Blood spots were collected by finger-prick from 316 clinically diagnosed measles patients in suburban Khartoum, mostly within a week after onset of the rash. Samples were collected between October, 2000 and April, 2003, and stored at 4 degrees C. Measles virus-specific IgM antibodies were detected in 200 (63%) of the samples using an "in-house" IgM capture ELISA. For 201 samples reconstitution and IgM measurement was repeated 1 year after initial testing with essentially the same results, showing the stability of IgM in the filter paper under these conditions. In a limited number of samples (n = 38) measles virus-specific IgM was also tested with a commercial indirect IgM ELISA. Although the results of the two assays correlated well, the "in-house" IgM capture ELISA proved slightly more sensitive. Measles virus-specific reverse transcriptase polymerase chain reaction (RT-PCR) amplicons were obtained from 16 of 57 (28%) samples tested. Sequencing of the 3' 456 nucleotides of the nucleoprotein gene showed the continued endemic circulation of genotype B3 viruses identified previously in this region. Although problems related to limited sample quantities were encountered, the present study confirms the usefulness of dried blood spots for measles surveillance. The results also demonstrate that measles continues to be endemic in the Sudan.

Genetic characterization of wild type measles virus isolated in Croatia during the 2003-2004 outbreak

Viral epidemiology is determined by the movement of infected people within and between geographical areas. The genetic characterization of wild-type isolates combined with standard epidemiological methods may enable the identification of the source and transmission pathways and permit differentiation between indigenous and imported viruses. We investigated the genetic characteristics of the wild-type measles virus isolated in Croatia during a 2003-2004 outbreak. The results of this study indicate the presence of the D4 measles virus genotype in Europe. The isolated virus is closely related to virus isolates from the India-like subgroup of the D4 measles virus genotype. The virus responsible for this outbreak differs in the hemagglutinin gene sequence from other virus strains belonging to the D4 genotype. The hemagglutinin gene sequence also differs when compared to viruses from other genotypes that are known to circulate in Europe and from vaccine strains.

Molecular epidemiology of measles virus in Kenya

Measles causes significant morbidity and mortality globally. Many countries have embarked on immunization programs to control and prevent measles outbreaks and eventually to eliminate endemic measles. Kenya is currently in the outbreak control and prevention stage for measles. Measles virus genotyping is important for molecular epidemiological purposes, including the documentation of the elimination of endemic measles virus strains from a country, and mapping of transmission pathways. In this study, we collected clinical specimens from measles outbreak cases in 2002 in Kenya for measles virus genotyping. We were able to isolate and/or detect measles virus in 10 cases from 5 of the 8 provinces in Kenya. All these Kenyan measles strains were determined to be genotype D4 strains when compared to the standard World Health Organization-designated measles virus reference strains. Interestingly, the Kenyan D4 strains clustered into two distinct D4 subgroups. In addition, the inclusion of other published D4 measles strains in this analysis indicated that there are four distinct D4 clusterings, or subgroups: Montreal-like, India-like, Johannesburg-like, and Ethiopia-like. This is the first measles molecular epidemiology study in Kenya and establishes the current endemic measles strain as genotype D4. Importantly, this study shows that the Kenyan D4 strains are distinct from the B3 measles strain found in West Africa and the D4 strains reported in Ethiopia.

The unfinished measles immunization agenda

Despite achieving and sustaining global measles vaccination coverage of about 80% over the past decade, worldwide measles remains the fifth leading cause of mortality among children aged <5 years. In May 2002, the United Nations Special Session on Children endorsed the goal of reducing measles deaths by half by 2005. Countries and World Health Organization (WHO) regions that adopted aggressive measles control or elimination strategies have shown excellent results. In 2001, countries in the Americas reported an all time low of 537 confirmed measles cases. Substantial progress in measles control has also been achieved in the WHO Western Pacific Region, in seven southern African countries, and in selected countries in WHO European, Eastern Mediterranean, and Southeast Asian regions. The ongoing measles disease burden and availability of safe and effective measles mortality reduction strategies make a compelling case to complete the unfinished agenda of measles immunization.